This invention relates generally to nondestructive testing and more particularly to an automatic eddy current inspection system having a dual trace output.
Eddy current inspections systems are known in the art and an automatic system is shown in U.S. Pat. No. 3,718,855 granted to us on Feb. 27, 1973. The invention presented herein is an improvement over our known system for the inspection of fastener holes.
When inspecting fastener holes there are many instances where the eddy current probe will pass through multiple layers of material. Although our known system will indicate a flaw in the material, it will also indicate the separation between layers of material. There is currently no known means for distinguishing between a flaw and the separation of layers of inspectable material. Further, there are times when uninspectable material may separate layers which need positive identification. Also, there is a need to be able to determine the orientation of flaws or cracks. Some cracks are radial which others are circumferential. Other flaws may be of the exfoliation type. Presently the determinations of type and size must be made visually with a separate process once it has been discovered.
In fastener hole inspection it is of significant importance to the structural engineer that he know the type and location of the defect. The corrective action required will depend in part upon the particular structural member affected since certain structural members are inherently more critical than others and require immediate attention to prevent disastrous failures.